Journal
ARDEOLA
Volume 61, Issue 2, Pages 297-309Publisher
SOC ESPANOLA ORNITOLGIA
DOI: 10.13157/arla.61.2.2014.297
Keywords
carbon; nitrogen; open air dump; regurgitates; seabirds; stable isotopes; sulfur; Tunisia
Categories
Funding
- MAEC-AECI grant
- AECI-PCI Spanish-Tunisian [A/2907/05, A/6165/06]
- MICIN, Spain [CGL 254 2008-05448-C02-01]
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The yellow-legged gull Larus michahellis is usually considered as an opportunistic species that depends on food derived from anthropogenic activity, such as garbage and fishery discards. However, although it has become a problematic species in many Mediterranean countries, there is still no information about its status in Tunisia. The aim of this work was to assess the differential use of marine and terrestrial resources by the yellow-legged gulls breeding in an urban area on Chikly Island. Dietary reconstructions were performed through the analysis of regurgitates and delta C-13, delta S-34 and delta N-15 of fledgling's feathers. Contrary to most Mediterranean breeding colonies, and to our expectations, the mixing model showed that yellow-legged gulls from Chikly are above all marine foragers. Whereas the Lake of Tunis was the principal source of food in 2005 and 2007, chicks from 2006 were fed mainly with prey from the Gulf of Tunis. Although the Gulf is located further from the breeding colony and has less fishing activity than the Lake, our study demonstrated that it is used as an alternative foraging habitat. The Bayesian mixing model approach proved to be a useful tool for evaluating temporal variations in the feeding ecology of the colony, which is a relevant information for the management of a wild species. This study also demonstrated the importance of isotopic variability among years for inferring diet diversity and food availability for the colony, thereby allowing demographic forecasts when trophic resources vary in abundance or the foraging habitat is disturbed.
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